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----------------------------------------------------------------------------- This file contains a concatenation of the PCRE man pages, converted to plain text format for ease of searching with a text editor, or for use on systems that do not have a man page processor. The small individual files that give synopses of each function in the library have not been included. There are separate text files for the pcregrep and pcretest commands. ----------------------------------------------------------------------------- PCRE(3) PCRE(3) NAME PCRE - Perl-compatible regular expressions INTRODUCTION The PCRE library is a set of functions that implement regular expres- sion pattern matching using the same syntax and semantics as Perl, with just a few differences. Certain features that appeared in Python and PCRE before they appeared in Perl are also available using the Python syntax. There is also some support for certain .NET and Oniguruma syn- tax items, and there is an option for requesting some minor changes that give better JavaScript compatibility. The current implementation of PCRE (release 7.x) corresponds approxi- mately with Perl 5.10, including support for UTF-8 encoded strings and Unicode general category properties. However, UTF-8 and Unicode support has to be explicitly enabled; it is not the default. The Unicode tables correspond to Unicode release 5.0.0. In addition to the Perl-compatible matching function, PCRE contains an alternative matching function that matches the same compiled patterns in a different way. In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the pcrematching page. PCRE is written in C and released as a C library. A number of people have written wrappers and interfaces of various kinds. In particular, Google Inc. have provided a comprehensive C++ wrapper. This is now included as part of the PCRE distribution. The pcrecpp page has details of this interface. Other people's contributions can be found in the Contrib directory at the primary FTP site, which is: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre Details of exactly which Perl regular expression features are and are not supported by PCRE are given in separate documents. See the pcrepat- tern and pcrecompat pages. There is a syntax summary in the pcresyntax page. Some features of PCRE can be included, excluded, or changed when the library is built. The pcre_config() function makes it possible for a client to discover which features are available. The features them- selves are described in the pcrebuild page. Documentation about build- ing PCRE for various operating systems can be found in the README file in the source distribution. The library contains a number of undocumented internal functions and data tables that are used by more than one of the exported external functions, but which are not intended for use by external callers. Their names all begin with "_pcre_", which hopefully will not provoke any name clashes. In some environments, it is possible to control which external symbols are exported when a shared library is built, and in these cases the undocumented symbols are not exported. USER DOCUMENTATION The user documentation for PCRE comprises a number of different sec- tions. In the "man" format, each of these is a separate "man page". In the HTML format, each is a separate page, linked from the index page. In the plain text format, all the sections are concatenated, for ease of searching. The sections are as follows: pcre this document pcre-config show PCRE installation configuration information pcreapi details of PCRE's native C API pcrebuild options for building PCRE pcrecallout details of the callout feature pcrecompat discussion of Perl compatibility pcrecpp details of the C++ wrapper pcregrep description of the pcregrep command pcrematching discussion of the two matching algorithms pcrepartial details of the partial matching facility pcrepattern syntax and semantics of supported regular expressions pcresyntax quick syntax reference pcreperform discussion of performance issues pcreposix the POSIX-compatible C API pcreprecompile details of saving and re-using precompiled patterns pcresample discussion of the sample program pcrestack discussion of stack usage pcretest description of the pcretest testing command In addition, in the "man" and HTML formats, there is a short page for each C library function, listing its arguments and results. LIMITATIONS There are some size limitations in PCRE but it is hoped that they will never in practice be relevant. The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is compiled with the default internal linkage size of 2. If you want to process regular expressions that are truly enormous, you can compile PCRE with an internal linkage size of 3 or 4 (see the README file in the source distribution and the pcrebuild documentation for details). In these cases the limit is substantially larger. However, the speed of execution is slower. All values in repeating quantifiers must be less than 65536. There is no limit to the number of parenthesized subpatterns, but there can be no more than 65535 capturing subpatterns. The maximum length of name for a named subpattern is 32 characters, and the maximum number of named subpatterns is 10000. The maximum length of a subject string is the largest positive number that an integer variable can hold. However, when using the traditional matching function, PCRE uses recursion to handle subpatterns and indef- inite repetition. This means that the available stack space may limit the size of a subject string that can be processed by certain patterns. For a discussion of stack issues, see the pcrestack documentation. UTF-8 AND UNICODE PROPERTY SUPPORT From release 3.3, PCRE has had some support for character strings encoded in the UTF-8 format. For release 4.0 this was greatly extended to cover most common requirements, and in release 5.0 additional sup- port for Unicode general category properties was added. In order process UTF-8 strings, you must build PCRE to include UTF-8 support in the code, and, in addition, you must call pcre_compile() with the PCRE_UTF8 option flag. When you do this, both the pattern and any subject strings that are matched against it are treated as UTF-8 strings instead of just strings of bytes. If you compile PCRE with UTF-8 support, but do not use it at run time, the library will be a bit bigger, but the additional run time overhead is limited to testing the PCRE_UTF8 flag occasionally, so should not be very big. If PCRE is built with Unicode character property support (which implies UTF-8 support), the escape sequences \p{..}, \P{..}, and \X are sup- ported. The available properties that can be tested are limited to the general category properti